Sine bars or sine plates are commonly employed in machine shops and the like for the inspection of single and compound angles on workpieces. While sine bar devices are well known for the measurement of simple angles, the checking and determination of compound angles of a workpiece presents a far more difficult situation.
Thus, typical prior art techniques for compound angle measurements may take one of three approaches in setting up the workpiece to be inspected:
Firstly, the inspector can use two separate sine bars, the two used in conjunction so as to bring the compound surface level. In practical terms, this is the common approach in most work environments.
A second approach employs a hinged type of compound sine plate wherein two plates are hinged to each other and permit the orientation of the compound surface to level position. This system is taught, for example, in U.S. Pat. No. 3,243,885 to D. W. Johnson.
The third approach employs three spheres to render an angled surface level. This is also taught in the aforesaid Johnson patent, as well as in U.S. Pat. No. 2,306,227 to G. Seidel.
There is need for a more reliable and simpler approach to sine bar measurement of compound angles, and further, for a sine bar that has the requisite geometry to make it trigonometrically possible to ascertain the vertical distance from a base surface to the compound surface under measurement.